1. Field
The disclosure relates to an electrode for solid-state batteries, a method of preparing the electrode, a solid-state battery containing the electrode, and a bonding film used for preparing the electrode.
2. Description of the Related Art
As published in Japanese Patent Publication No.1998-125330, Japanese Patent Publication No.1993-13099, Japanese Patent Publication No. 2008-257962 and Japanese Patent Publication No. 2011-134675, as lithium ion secondary batteries, solid-state batteries using a solid electrolyte are known. Such solid-state batteries include an electrolyte layer including the solid electrolyte, electrodes (a positive electrode and a negative electrode) formed on both surfaces of the electrolyte layer, and a current collecting member attached to each of the electrodes. The solid-state batteries use solid electrolytes as the electrolytes thereof, and generally, the solid electrolyte is also mixed in each of the electrodes.
As a method of preparing solid-state batteries, a powder compression molding method includes adding powder materials that sequentially form each layer to a cylindrical container, compression molding the powder materials and sealing both ends of the container with current collecting members. However, when the powder compression molding method is used, an electrode area may not be efficiently increased as a different container and a different pressing apparatus are used based on a size of the electrode area, in which the electrode area means the area of which the electrode is in contact with the electrolyte layer. Thus, the powder compression molding method may not be efficiently used for increasing capacity of a solid-state battery.
Thus, a coating method of preparing a solid-state battery has been proposed that includes forming a coating composition for each layer by mixing a powder material of each layer, a binder and a solvent, forming a stacked structure by sequentially coating the coating composition on the current collecting member and drying, and rolling the stacked structure. The coating method of preparing a solid-state battery may easily increase the electrode area by simply enlarging the size of the coating areas of the electrode and the electrolyte layer.
However, characteristics of the solid-state battery prepared by the coating method may degrade when the solid electrolyte used is highly reactive, such as a sulfide-based solid electrolyte. Specifically, the sulfide-based solid electrolyte degrades as the sulfide-based solid electrolyte reacts with the binders or solvents used in the electrode of a lithium ion secondary battery which includes a non-aqueous liquid in the electrolyte thereof.
Therefore, Japanese Patent Publication No. 2011-134675 has proposed using a binder or a solvent that is inactive to a solid electrolyte. However, the electrode and the current collecting member may not be substantially bound, thus the current collecting member may be peeled off from the electrode during, for example, rolling of the electrode.
In addition, according to a technical feature disclosed in Japanese Patent Publication No. 2008-257962, a conductive layer is interposed between a current collecting member and an electrode layer, and the current collecting member and the conductive layer are bound with a conductive bonding material containing ethyl acetate. Ethyl acetate is a compound including a polar functional group. Therefore, the current collecting member and the conductive layer are expected to be sufficiently bound to each other. However, the technical feature disclosed in Japanese Patent Publication No. 2008-257962 does not use a binder in the positive electrode layer.